1. Field of the Invention
The present invention relates to data communication systems and, more particularly, to data communication systems that provide different services over a common channel.
2. Description of the Related Art
Often, with conventional communications systems, communication channels are shared by different devices that operate on the same channel. In conventional Asymmetric Digital Subscriber Line (xe2x80x9cADSLxe2x80x9d) transceivers (i.e., modems) it is common to use two pairs of xe2x80x9csplitterxe2x80x9d filters to separate Plain Old Telephone Service (POTS) and ADSL services that operate on the same line. One pair of the splitter filters is provided at the central side and the other pair is provided at the remote side. Each pair of splitter filters includes a low pass filter that passes signals to the POTS and a high-pass filter that passes signals to the ADSL services.
FIG. 1 is a block diagram of a data communication system 10 in which a communication channel (i.e., line) supports both POTS and ADSL services. The data communication system 10 includes a central side 12 and a remote side 14. The central side 12 is, for example, a central office, and the remote side 14 is, for example, associated with a customer""s premises (e.g., business or residential premises).
The central side 12 includes a DMT transceiver 16 and a telephone network 18. The DMT transceiver 16 includes a DMT transmitter 20, a DMT receiver 22, and a hybrid circuit 24. The DMT transmitter 20 operates to transmit data over the channel through the hybrid circuit 24. The DMT receiver 22 operates to receive data that has been transmitted over the channel and received through the hybrid circuit 24. The central side 12 also includes a splitter 26 (i.e., pair of splitter filters) that passes lower frequency signals incoming over a line 28 to the telephone network 18 and passes higher frequency signals incoming over the line 28 to the hybrid circuit 24.
The remote side 14 includes a DMT transceiver 30 and a customer telephone service 32. The DMT transceiver 30 includes a DMT receiver 34, a DMT transmitter 36 and a hybrid circuit 38. The remote side 14 also includes a splitter 40 (i.e., pair of splitter filters) that is coupled to the line 28 as well as to the customer telephone service 32 and the hybrid circuit 38. The splitter 40 operates to pass incoming signals from the line 28 to either the hybrid circuit 38 or the customer telephone service 32. If the incoming signals over the line 28 are low frequency signals, then the splitter 40 forwards the signals to the customer telephone service 32. On the other hand, if the incoming signals over the line 28 are higher frequency signals, the splitter 40 forwards the signals to the hybrid circuit 38 of the transceiver 30.
Accordingly, the data communications system 10 is able to provide ADSL and POTS services over the same line (i.e., the line 28). The splitters 26 and 40 operate to filter the differing services appropriately so as to direct signals to the proper service. Additional details on ADSL can be found in American Nationals Standard Institution (ANSI) published standard ANSI T1.413-1995 pertaining to Network and Customer Installation Interfacesxe2x80x94Asymmetric Digital Subscriber Lines (ADSL) Metallic Interface, which is hereby incorporated by reference.
There are, however, several problems associated with the conventional design of the data communication systems supporting multiple services over a common communication channel. One problem of a remote ADSL transceiver (such as the remote transceiver 30 illustrated in FIG. 1) is that a low-pass filter associated with the splitter (e.g., the splitter 40) needs to be installed near the entrance of the line (e.g., the line 28) to the customer""s premises. As noted above, the design of the splitter includes two filters (i.e., splitter filters), one filter (high-pass filter) is formed in or coupled to the transceiver (i.e., the transceiver 30) and the other filter (low-pass filter) is installed at the entrance of the line to the customer""s premises. The installation of such a filter (i.e., low-pass filter) at the customer""s premises is inconvenient and burdensome to both customers and telephone service providers.
Some data communication systems have tried to remove the low-pass filter associated with the splitter at the remote side. While this avoids the inconvenience and burden of having to install the low-pass filter at the customer""s premises, doing so causes high levels of noise to be generated at the telephone at the customer""s premise which impedes its use and is otherwise unsatisfactory to users. More particularly, in the case of ADSL transceivers using discrete multi-tone (DMT) modulation, when a customer transmits data upstream (i.e., toward a central office) using a DMT modulation technique without having a low-pass filter of the splitter at the customer""s premises, non-linearities in the circuitry of many telephones can cause intolerably high levels of noise to be generated by the telephone""s speaker and heard in the telephone""s earpiece.
Another approach that has been proposed to solve the noise problem that results in an ADSL system without the low-pass filter associated with the splitter at the customer""s premises is to transmit at lower power levels or use a less effective modulation technique. Transmitting at lower power levels significant drops the available data rates that can be supported. While DMT modulation does (at high power levels) provided high data rates, it uses high frequency signals that have high signal strengths. These resulting high signal strengths, as noted above, give rise to the undesired noise at the customer""s telephones. A less effective modulation technique would use signals that have lower signal strengths or frequencies and thus produce less noise. However, the use of a less effective modulation technique in place of DMT also reduces the performance of the system in terms of its available data rate.
Thus, there is a need for improved techniques that allow telephone service and ADSL service to operate on the same line without requiring a low-pass filter portion of a splitter at a customer location.
The invention relates to a data communication system that provides different types of service to a remote site even when the remote site lacks a splitter. A central site (e.g., central office) is able to communicate with at least two different types of remote sites. One type of remote site includes a full splitter (i.e., both low-pass and high-pass filters), and the other type of remote site has only a partial splitter (i.e., includes high-pass filter but lacks a low-pass filter). Although conventionally the transceivers (e.g., ADSL transceivers) at these remote sites would be of the same design and use the same modulation technique for upstream as for downstream transmissions, here the remote site that lacks a low-pass filter (i.e., partial splitter type remote site) uses a different modulation technique for upstream transmissions. As an example, the remote site without a complete splitter could use continuous phase modulation (CPM) for upstream transmissions and discrete multi-tone (DMT) for downstream transmissions. More generally, while a high peak-average-ratio (PAR) technique like DMT can be used on downstream transmissions that do not lead to noise at the telephone service even in the splitterless design, a lower PAR technique (e.g., CPM, QAM, FSK, etc.) can be used on the upstream transmissions so that the noise levels produced at the telephone service are vastly reduced. The central site is able to communicate with both the different types of remote sites. The central site selects from various receiver units depending on the type of modulation (e.g., low PAR technique) used by the remote sites.
The invention can be implemented in numerous ways, including as an apparatus, system, method, or computer readable media. Several embodiments of the invention are discussed below.
As a transceiver apparatus for data communications over a wire, an embodiment of the invention includes: a transmitter that provides data transmission service using a high PAR type modulation to transmit data; a first receiver capable of demodulating signals having a high PAR type demodulation to receive data; a second receiver capable of demodulating signals having a low or intermediate PAR type demodulation to receive data; and a switch unit operatively connected to select one of the first and second receivers to receive the incoming data transmission service communications from the wire.
As a data communication system that shares transmission lines for both telephone service and data transmission service, one embodiment of the invention includes a central side for providing the telephone service and the data transmission service, and a remote side for providing the telephone service and the data transmission service. The remote side couples to a telephone service device. The central side includes: a central-side transmitter that provides data transmission service using first type modulation to transmit data; a central-side receiver that provides data transmission service configured to use either first type demodulation or second type demodulation to receive data; and a splitter circuit coupled to a transmission line. The splitter circuit directs incoming telephone service communications over the transmission line to a telephone network and directs incoming data transmission service communications over the transmission line to the central-side receiver, and couples outgoing telephone service communications and outgoing data transmission service communications to the transmission line. The remote side includes: a remote-side receiver that provides data transmission service using first type demodulation to receive data; and a remote-side transmitter that provides data transmission service using either first type modulation or second type modulation to transmit data. When the remote-side transmitter provides data transmission service using first type modulation, the central-side receiver is configured to use first type demodulation, and when the remote-side transmitter provides data transmission service using second type modulation, the central-side receiver is configured to use second type demodulation.
As a data communication system that shares transmission lines for both telephone service and high-speed data transmission service, another embodiment of the invention includes: a central side for providing the telephone service and the high-speed data transmission service, and a first remote side for providing the telephone service and the high-speed data transmission service. The remote side couples to a telephone service device. The central side includes: a central-side transmitter that provides high-speed data transmission service using first type modulation to transmit data; a central-side first receiver that provides high-speed data transmission service using first type demodulation to receive data; a central-side second receiver that provides high-speed data transmission service using second type demodulation to receive data; a switch unit operatively connected to select one of the central-side first receiver and the central-side second receiver to receive the incoming high-speed data transmission service communications; and a splitter circuit that directs incoming telephone service communications over the transmission line to a telephone network and directs incoming high-speed data transmission service communications over the transmission line to the switch unit, and couples outgoing telephone service communications and outgoing high-speed data transmission service communications to the transmission line. The first remote side includes: a high-pass filter circuit that passes the incoming high-speed data transmission service communications from the transmission line and blocks the telephone service communications from the transmission line; a remote-side first receiver that provides high-speed data transmission service using first type demodulation to receive data; and a remote-side first transmitter that provides high-speed data transmission service using second type modulation to transmit data. Preferably, the remote side lacks a low-pass filter circuit coupled to the telephone service device. Optionally, the first type modulation uses discrete multi-tone modulation and the first type demodulation uses discrete multi-tone modulation, and the second type modulation uses continuous phase modulation and the second type demodulation uses continuous phase demodulation.
As a data communication system that shares transmission lines for both telephone service and high-speed data transmission service, still another embodiment of the invention includes: a central side for providing the telephone service and the high-speed data transmission service, and a remote side for providing the telephone service and the high-speed data transmission service, the remote side couples to a telephone service device. The central side includes: a central-side DMT transmitter that provides high-speed data transmission service using multicarrier modulation to transmit data; a central-side DMT receiver that provides high-speed data transmission service using multicarrier demodulation to receive data; a central-side CPM receiver that provides high-speed data transmission service using continuous phase demodulation to receive data; a splitter circuit coupled to a transmission line, the splitter circuit directs incoming telephone service communications over the transmission line to a telephone network and directs incoming high-speed data transmission service communications over the transmission line to the central-side DMT transceiver, and couples outgoing telephone service communications and outgoing high-speed data transmission service communications to the transmission line; and a switch unit operatively connected to select one of the central-side DMT receiver and the central-side CPM receiver to receive the incoming high-speed data transmission service communications from the transmission line. The remote side includes: a filter circuit operatively coupled to the transmission line, the filter circuit passes the incoming high-speed data transmission service communications from the transmission line and blocks the telephone service communications from the transmission line; a remote-side DMT receiver operatively coupled to the filter circuit, the remote-side DMT receiver provides high-speed data transmission service using multicarrier demodulation to receive data; and a remote-side CPM transmitter operatively coupled to the filter circuit, the remote-side CPM transmitter provides high-speed data transmission service using continuous phase modulation to transmit data.
The advantages of the invention are numerous. One advantage of the invention is that undesirable noise level that conventionally appears in telephones when the remote side uses splitterless operation are eliminated or substantially reduced by the invention. Another advantage is that the central side can support either splitter or splitterless operation with a common design, the receiver(s) in the central-side are simply configured for respective remote sites depending on whether the remote site has a splitter or not (or depending on the modulation technique utilized). Yet another advantage is that by using hybrid transceivers with splitterless operation, the downstream transmissions continue to use higher performance modulation techniques (e.g., DMT), whereas upstream communications can use a modulation technique with less performance (e.g., CPM) to reduce the undesired noise.